1. Field of the Invention
The present invention relates to an extended nip press apparatus for removing water from a web. More particularly, the present invention relates to a press apparatus having an elongate shoe defining a concave surface having a pocket therein.
2. Information Disclosure Statement
Extended nip presses enable the residence time of the web within a press nip to be increased so that more water is able to be removed from the web.
Basically, extended nip presses fall into two categories as follows: 1) Hydrodynamic; 2) Hydrostatic. First, a hydrodynamic press includes a hydrodynamic shoe. The shoe defines a concave surface which cooperates with a rotatable backing roll such that a bearing blanket is able to slidingly engage the concave surface for supporting the web during passage through an extended nip. Lubricant is supplied between the bearing blanket and the concave surface in order to permit the blanket to slide along the concave surface.
Second, several hydrostatic presses have been proposed in which the aforementioned concave surface of the shoe defines a pocket so that at least for a portion of the travel of the blanket through the extended nip, the blanket is hydrostatically supported by a lubricant within the pocket.
More recently, as exemplified in U.S. Pat. No. 5,262,011 to Ilmarinen, wedge-shaped pockets have been proposed in which the trailing end of the pocket decreases to a zero depth. One of the objectives of the wedge- shaped pocket is to inhibit damage of the blanket in the event of a wad of the web entering the extended nip. Such wad would tend to be received within the hydrostatic pocket. However, if the hydrostatic pocket abruptly terminates at the trailing end thereof, there is a tendency for the wad to cause a sudden pressure surge as the wad tends to move between the blanket and the concave surface at the trailing end of the pocket.
The aforementioned U.S. Pat. No. 5,262,011 is provided with channel means for supplying pressurized lubricant to the hydrostatic pocket. Applicant has discovered that the aforementioned pocket has a comparable performance, even when lubricant is not supplied to the pocket by independent lubricant supply means. Therefore, the provision of costly ancillary equipment, such as pumps, control valves and piping, is avoided.
Moreover, Applicant has discovered that sufficient lubricant flows from the concave surface disposed upstream relative to the pocket into the pocket in order to provide support for the bearing blanket moving through the extended nip.
Therefore, it is a primary objective of the present invention to provide an extended nip press apparatus having an elongate shoe with a concave surface that encompasses a pocket. The arrangement is such that the pocket is filled with lubricant flowing from the concave surface so that in the event of a wad of the web entering into the extended nip, the wad is yieldingly received within the pocket so that damage to the blanket by the wad is minimized.
Other objects and advantages of the present invention will be readily apparent to those skilled in the art by a consideration of the detailed description contained hereinafter, taken in conjunction with the annexed drawings.